Field of the Invention
This invention relates to needle shield arrangements and to injection apparatus incorporating such arrangements. It is known to provide a syringe shield to cover the needle of a syringe prior to injection to maintain sterility of the needle, to avoid evaporation of a medicament contained within the syringe, to prevent needle stick injuries and also to protect the needle during manufacture and assembly of injection devices. In a known form of rigid needle shield arrangement, a soft rubber inner boot fits over a ribbed spigot at the forward end of the syringe body and the boot is contained by an outer rigid cylindrical portion. In such arrangements, the needle shield is a slip fit over the spigot and there is no connection between the shield and the syringe body.
Description of the Related Art
In addition, in autoinjector devices where a syringe or cartridge is initially driven forwardly in a penetration phase to insert the needle into the flesh, there is usually some arresting action on the syringe when it is in its forwardmost position. Often, that arresting force is passed to the syringe flanges either directly or via a cylindrical syringe carrier or the like. Because the flanges extend at right angles to the barrel of the syringe, the angle acts as a stress magnifier and there is a risk that the flange breaks off so that the syringe shoots forwardly beyond its required position. Also, we have found that, because of an accumulation of tolerances the tolerance of the distance between the needle tip and the flange surface is relatively large. Since the movement of the syringe, the penetration depth of the needle and other injection characteristics are affected by the accumulated tolerance between the reference surface on the syringe and the needle front tip, it is important to reduce this. The accumulated tolerance would be reduced if the forwarding facing load-bearing surface on the syringe were forwardly of the flange. It is also preferred to pass the restraint load into the cylindrical wall of the syringe in axial alignment with the wall, not only to reduce offset loads but also to allow the diameter of any arresting surface or spring to be relatively high so as not to obstruct the area in front of the syringe which may house an arresting spring, a needle shield remover and so on.
GB2424836 discloses an injection device in which a tamper-evident needle shield is connected to a needle hub by a frangible connection. The needle hub is a separate item fitted onto the tip of the syringe rather than the body thereof. There is no suggestion of reacting any restraint load via the portion of the needle hub that remains after removal of the needle shield.
GB2425062 discloses in FIGS. 6 and 7 an injection device in which a needle cap connected to a needle sub-assembly by a frangible connection. The needle sub-assembly is fitted onto the tip of the syringe. There is no disclosure of any needle shield arrangement in which a shield portion is frangibly connected to a portion that engages the main body of the syringe, nor of an arrangement in which the syringe engaging portion receives all or part of the arresting load as the syringe is arrested at the end of its extension movement.
U.S. Pat. No. 6,053,892, WO03/095002 and GB927626 each disclose a hypodermic syringe head with a tamper-evident seal. Again, this has a hub that fits onto the tip of the syringe.